1. Field of the Invention
The present invention relates to a black matrix which is used for manufacturing color picture tube or color display tube, and more particularly, to a process for preparing a black matrix where clear black matrix dots can be produced by etching graphite effectively.
2. Description of the Related Art
In the conventional process for preparing a black matrix which is used for manufacturing a CPT (Color Picture Tube) or a CDT (Color Display Tube), a photoresist such as PVP and DAS, PVA and ADC, polyvinyl alcohol is uniformly coated on a substrate, i.e., a panel, and the photoresist is dried by heating and then exposed to ultraviolet rays on the substrate provided with a mask assembly through mask slots, as shown in FIG. 4. The exposed substrate is separated from the mask assembly, washed with distilled water, developed by removing unexposed photoresist, and dried. Graphite solution is uniformly coated on the inside of the panel on which the photoresist-coated portion and the photoresist-uncoated portion are regularly arranged. Subsequently, graphite-coated photoresist is removed using an etching solution such as sulfuric acid, sulfonic acid, hydrogen peroxide, chloromatic acid, etc., to produce a black matrix. In this conventional process for preparing a black matrix, photoresist dots formed by exposing and developing have a flat shape in the central portion, whereas they have a tilt shape (5) in the circumference as shown in FIG. 5. Accordingly, imperfect etching of black matrix dots may occur as shown in FIG. 6.